Cold-applied asphalt compositions have demonstrated wide utility as sealants, cements, and a variety of coating materials. Compositions of this sort are characterized by the presence of an asphalt base, either neat, "cut-back" by a suitable solvent, or emulsified in water. The primary objective is to provide a product which meets specific performance standards and may be used without an external source of heat over a wide range of weather and application conditions.
With respect to this last requirement, an assortment of additional ingredients may be incorporated into the asphalt to achieve and/or improve performance characteristics. Fibers (synthetic and otherwise), fillers, pigments, and various miscellaneous chemical additives such as dispersants and surfactants may be included. These compositions may be further modified through selection of an asphalt base having a particular viscosity, softening point, and penetration. The asphalt cures after application, leaving a product designed and formulated to perform a specific function.
For many years asbestos has been used to impart texture, strength, and thixotropic properties to asphalt compositions. However, because indications are that asbestos is both toxic and carcinogenic many such products have fallen out of favor, especially so where comparable filler and/or fiber substitutes are available.
The search for improved cold-applied asphalt compositions where the asbestos used may be minimized or replaced entirely without a decrease in performance has been an on-going concern in the art. Asbestos may be replaced by a gelling clay, either alone or with a surfactant, to gel and thicken the asphalt. Other approaches utilize cellulose or synthetic fibers to prevent component separation within the asphalt composition and provide other desirable structural and physical characteristics.
However, the prior art has associated with it a number of significant problems and deficiencies. Most are related to inefficient formulation procedures and inadequate compositional performance, and result from the asphalt, filler, and fiber components currently used.
Where asbestos is avoided, one major problem of the prior art is sufficient dispersion of a suitable fiber substitute. Those fibers used tend to agglomerated as a result of manufacturing and packaging processes. An aqueous surfactant or an acrylic latex emulsion is often needed to disperse the fibers and promote a homogeneous product. Alternatively, special equipment is often required to de-lump or shred the fibers prior to addition. Once incorporated, the fibers tend to float, remain agglomerated, and/or resist wetting-out and dispersion. Some fibers, such as the cellulosics, once added, require additional time to reach an absorptive equilibrium with the host asphalt composition. Pre-soaking cellulose fibers in water or a surfactant has been suggested, but has achieved little practical utility. Likewise, high-speed and/or prolonged mixing may improve product consistency, but are often impractical. As a result, factors such as these adversely effect product formulation, necessitating adjustments to asphalt concentration and other composition components.
Likewise, with or without asbestos, if mineral fillers are used to impart certain physical properties to the asphalt composition, care must be taken to avoid uneven blending which may lead to a non-homogeneous product and subsequent performance deficiencies. For example, asphalt adheres very poorly to unwetted, dry filler particles. Poor adhesion later manifests itself in structural flaws and eventual composition failure.
Another significant concern relates to the asphalt currently used. Whether present neat, as a cutback, or in an emulsified form, a "harder" asphalt is desirable for its thixotropic and thermal resistance properties. However, softer asphalts are often favored for reasons relating to cost and formulation. The harder asphalts typically require higher operating temperatures, which may present a significant problem with respect to emulsion compositions where temperatures below 190.degree. F. are required to minimize water vaporization and prevent agglomeration. As a result, if harder asphalts are used, a chiller/cooler apparatus is required on the discharge port of the emulsion mill.
A concurrent problem relates to the accumulation of asphalt roofing wastes, the magnitude of which may be illustrated by just one component thereof - roofing shingles. According to a recent estimate, approximately 92 million squares of roofing shingles, each weighing between 200-250 pounds, are produced annually in the United States. Significant waste accompanies shingle manufacture and is estimated to total nearly 100,000 tons of shingle cut-outs/trimmings, corresponding to about 25,000 tons of asphalt. Similar quantities of broken and defective shingles and/or asphalt are also discarded. In addition, the annual removal of previously-applied shingles accounts for approximately 32 million tons of asphalt.
These figures are nearly matched by the amounts of waste generated from other types of asphalt roofing materials, such as asphalt-saturated organic felts, asphalt-impregnated glass and polyester mats, rolled roofing products such as ply sheets, modified bitumen membranes and the like, as well as commercial built-up roofs. (For the purpose of this discussion, the term "asphalt roofing wastes" will refer to waste generated through the manufacture and/or disposal of these and related materials.)
For many years, asphalt roofing wastes have been land-filled. What once seemed to be a sound "solution" has spawned a multitude of more worrisome concerns, foremost among which is the creation of permanent, non-reclaimable landfills. Furthermore, with an increasingly larger population and ever-growing volume of solid wastes, the number of available landfills has dwindled to the point where most states now ban certain types of refuse. As such, it is no longer environmentally-wise or economically-feasible to continue landfill disposal of asphalt roofing wastes.